The jump from Monarch to Emperor is pretty big, especially with the AI and spawning madness in Wildmana.
Tips below. This is, of course, my own play style (which clearly works but is not necessarily the "optimal" style). I almost always play Emperor, normal speed, PerfectWorld2 map (options: allow Pangaea, start anywhere), standard size map (PerfectWorld maps are "big" so this is really large), ~12 total civs, no tech brokering (otherwise I rely entirely on tech brokering to keep up), with many of the neat toys turned on (deadly wildmana, dragons, houses, passive training, etc.). The maps sometimes give Pangaea (maybe ~33%), mixed continents/islands with interconnecting "sea bridges" (33%) or an isolated island start (33%). (I'd like to say here that I really love these maps. They each seem so unique and surprising.)
Phase I (turn 1 - 50 or so): Explore and Grow. You have some safe time here before the baddies show up, so get that scout out exploring. Even your single warrior can do a ~15 tile loop and safely return home (use him to spot goody huts for your 2nd scout). You should strongly consider building a 2nd scout to take advantage of the safe time, but this can be risky. By the end of this period you should have (and constantly maintain) the maximum number of "no upkeep" units (8 - 9) which are mostly warriors. Initial build order is really situational depending on available food tiles:
1) If any available sea food. Research Fishing first; build 1 scout, 2+ warriors (until Fishing), workboat(s), then worker, then warriors until you are paying -1 or so for upkeep. One nice advantage here is that the baddies have nothing to pillage for a while -- they are forced to attack you in your city.
2) No seafood, but one or more 3 food tiles. Build warrior, then worker (micromanage to grow to 2 just before you complete warrior), then warriors until maxed out.
3) No seafood, no 3 food tiles. Build worker first (with -10% food penalty, it will be 20 turns before you grow to 2, and then the worker will actually take longer to build); then warriors till maxed out.
4) No food tiles to develop. You really need to move that settler somewhere else, or consider a restart.
Phase II (turn 50 - 150): Keep a low profile and get some COMMERCE!
Be content in one city for a while. It's much easier to defend 1 city with 8 warriors than 2 cities with 4 each, or 4 cities with 2 each (those additional small cities don't gain you much, if anything, in "free upkeep" units). You will move through the tech tree faster with fewer cities. I also strongly suspect (although I don't know for sure) that a higher unit/city ratio makes you a less appealing target for other civs and wandering baddies, even when your comparative strength is a pathetic 0.2 (as it will be at this stage). Consider building 2nd city when: 1) you are swimming in excess food and 2) that 2nd city will provide some specific benifit NOW (e.g., adds happy resource(s) or copper and/or will overcome its cost by providing additional commerce NOW). Unfortunately, you have no choice now except to churn out warriors to replace the dead. They are cheap to produce and effective at high numbers, although also expensive to maintain at high numbers. I'll wait until my settler is 1 turn from completion, then churn out 5 (2-turn production) warriors for escort (you can delay completion of a unit for 10 turns without loss). So you may go to +5 on unit upkeep but this will only last a short duration as those warriors get beat down. Do your best to protect promoted units by sacrificing new ones. Keep a very close eye on unit maintanance. You may want to go into the +5 to +10 territory breifly (e.g., if Orthus is around) but you NEVER should have less than the max that have free upkeep.
Your first priority for your tiny 1 or 2 city empire (after eating and surviving, of course) is to get some COMMERCE. I would prioritize in this order:
1) Tech apporpriately and develop commerce tiles first (no brainer here if you have gold available). One or two fishing villages may be your first (and very good) real commerce producers.
2) Get Mystisism and go God King (really potent if you are focusing on one-city development), build Elder Counsel.
3) Trade! Don't underestimate this. A trade route plus lighthouse gets you +6 or so commerce at this stage (better than a gold mine without having to dedicate a citizen). Get two explores out quickly to circumnavigate your continent. Get sailing, get cartography (or not, if you have trade partner that already has it, which is common at Emperor), then keep trade-increasing techs and buildings high on your priority list (trade, currency, lighthouses, harbors, inns, etc.; especially keep in mind build bonuses for Organized or other leader traits). (I would have said here that the Great Lighthouse is a must, but this will require Optics in 9.0.)
4) Settle an early prophet. You might get one early by event or if you go for 2 specialist economy early (which may be worth it if you are Philosophical or go Pacifisism after maxing out warrior production) and it has a big effect at this stage.
5) Cotteges. You really can do without these if you have #1 or 3 above. But this may be your only option. Good luck defending cottages at this early stage.
6) Religion. Always develop something from 1-4 before this. The ONLY religous beeline I ever do is Lanun OO, and that is only because commerce is completely taken care of with fishing. And in any case, you will need to open trade routes before a religious holy city can pay much. In the special case of OO, consider delaying your 2nd city so that your capital is the holy city.
Phase III (turn 150 - 250): Don't get your @$$ kicked. Os-Gabella and/or Mahala will be stopping by to say hello in the early part of this phase. You should be looking toward winding down the warrior-for-the-meatgrinder production as your primary means of defence. Get out a single early hero (Severous, Rosier, Rantine, etc.) and some other early but effective troops (copper weapon-promoted axemen, a stack of death I adepts, hunters that have been well-experienced capturing animals, etc.). Consider shifting to Military State to reduce unit upkeep as your cities and army start to take off (also to allow rush buying). Remember, you don't need every possible unit in every game. Think about what you really need. I won't go into any military detail here; there are so many options and it is completely situational depending on your civ, available resources, and neighboring civs. The main point is that your particluar advantages are known and the coming challenges are very PREDICTABLE. If Sheaim are near, they will come for you. What will you do to counter them? You need to ask yourself this question long before it actually happens. Establish some means of early detection (hunter-bird is one, but not the only, option) and some means to counter (e.g., a flatland killing zone for your horsemen). You might need to declare war before they reach your borders. Your really should not be surprised by what comes. Don't over-build your military (you want to be using that gold for development). In most cases, you can still use last-minute, massive-warrior-production as part of your defence (that pyre zombe SOD might take 10, 20 turns to reach you after you see it). Consider (even if you are a builder) kicking some @$$ yourself after you face the onslaught. It's a good time to take a city after you have just killed their main SoD (but watch out! another civ might also be coming for a visit; this is why I often wait for phase IV for serious conquest). On the naval side, where pirates are the only real threat, put one trireme (buckaneer crew) on each resource and fishing village; replace as necessary (pirates are not that tough, really).
Phase IV (turn 250 and beyond): Pick one of many "overpowered" features and go with it. If you survive the onslaught in phase III (or by some luck of your starting position, it never happened), you are now well placed to conquer, develop super cities, or whatever floats your boat. I usually see my relative power ranking go from a low of 0.2 (early phase III) to about 1.0 by turn 270 or so, and then very quickly to 2, 3, and beyond (I've got my dedicated city with Heroic Epic cranking out units now). The basic idea is that there are many "overpowered" features in FFH (and mods thereof) both related to military and economy. Just pick one and go with it. Want a size 50 (non-fallow) super city with 12 trade routes? Play Mortmorgan. Sooo many options. If you survive phase III and are not now pulling ahead (or at least neck-and-neck) with the top AI civs, then you are doing something very wrong. In truth, I generally quit about turn 270 because I know (from much experience) that there will be no further surprises or challenges.
Edit: acantoni, I'm just guesstimating that turn 70 on quick speed, small map, puts you about turn 150 on my scale above (late phase II / early phase III). Of course, things just play very differently at different speeds. There is a point in the game that you just can't be ready for those stacks.